* Government condemns "mass murderers"
* Bombings among region's biggest attacks in recent years
* Abu Sayyaf militants suspected of involvement
* Sulu voters opposed autonomy in plebiscite
The Philippines vowed to destroy those behind twin bombings that killed 27 people during a Sunday church service in the country's restive south.
The attack wounded 77 and was one of the deadliest in recent years in a region long plagued by instability. It came amid hope and excitement about the ratification of a devolution plan that aims to bring development, jobs and peace to one of Asia's poorest and most volatile places.
The first explosion went off inside the cathedral on Jolo island, in Sulu province, and was followed by a second blast outside, that was detonated as security forces raced to the scene, officials said.
"The enemies of the state have boldly challenged the capability of the government to secure the safety of the citizenry in that region," said Salvador Panelo, spokesman of Philippine President Rodrigo Duterte.
"The armed forces of the Philippines will rise to the challenge and crush these godless criminals."
There was no immediate claim of responsibility but police suspect the bombings were the work of the Abu Sayyaf, a militant group that has pledged allegiance to Islamic State and is notorious for its bombings and brutality.
"They want to show force and sow chaos," national police chief Oscar Albayalde told DZMM radio, suggesting the Abu Sayyaf group was the prime suspect.
Jolo is a stronghold of the Abu Sayyaf, which runs a lucrative piracy and kidnapping operation that successive governments have failed to break up. The group, which operates in the waters and islands of western Mindanao, has beheaded numerous foreign captives when ransom payments were not met.
Pictures distributed by the military of the inside of the Jolo church showed several rows of wooden pews destroyed, with debris strewn across a blackened floor. Humvees and army trucks were lined up on the road outside.
Defence Secretary Delfin Lorenzana called the attack a "dastardly act" and urged the local population to cooperate and "deny terrorism any victory".
National Security Adviser, Hermogenes Esperon, called those responsible "mass murderers" and "extremist criminals".
"We will not allow them to spoil the preference of the people for peace," he added.
Civilians bore the brunt of the attack, which also killed seven soldiers. Sixty-one civilians were among those wounded.
The Philippine military in mid 2017 encountered its biggest and longest battle since World War Two when an alliance of extremists loyal to Islamic State, among them foreigners and children, overran Marawi City and tried to establish a caliphate.Last updated: January 27 2019 12:03 PM